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Abstract:

A process to convert glycerin into propylene glycol and purifying the
produced propylene glycol is described. The glycerin-based propylene
glycol production requires only one process step compared to
petroleum/natural gas-based propylene glycol production requires multiple
process steps, and thus represents a cost savings.

Claims:

1. A process for converting glycerin into propylene glycol comprising the
steps of: preheating a feed mixture comprising glycerin, hydrogen and
methanol in a reactant heater; passing the heated feed mixture to a
reactor; separating the reactor effluent into a vapor phase stream and a
liquid phase stream; condensing the vapor phase stream into a condensed
liquid; recycling the condensed liquid to the reactor; and distilling the
liquid phase stream to obtain purified propylene glycol.

2. The process according to claim 1, wherein the reactor is a fixed bed
reactor.

3. The process according to claim 1, wherein the reactor is operated at a
temperature of 150.degree. C.-240.degree. C.

4. The process according to claim 1, wherein the reactor is operated at a
pressure of 20-80 atmospheres.

5. The process according to claim 1, further comprising hydrogenating the
heated feed mixture in the reactor.

6. The process according to claim 5, wherein the hydrogenating is carried
out by a supported catalyst in the fixed bed reactor.

7. The process according to claim 6, wherein the supported catalyst is a
metal or metal oxide catalyst.

8. The process according to claim 7, wherein the supported catalyst
comprises copper.

9. The process according to claim 1, further comprising mixing the
condensed liquid with a glycerin feed.

10. The process according to claim 1, wherein the liquid phase stream is
depressurized and cooled prior to distilling.

11. The process according to claim 1, wherein the liquid phase stream is
distilled in multiple distillation columns.

Description:

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This Application claims the benefit under 35 U.S.C. 119(e) of U.S.
Provisional Patent Application Ser. No. 61/451,246 filed Mar. 10, 2011,
which is incorporated herein by reference in its entirety as if fully set
forth herein.

FIELD OF THE INVENTION

[0002] This invention relates to a process for converting glycerin to
propylene glycol and purifying the propylene glycol that is produced.

BACKGROUND OF THE INVENTION

[0003] The world is collectively engaged in a massive search for energy
alternatives to ever higher priced crude oil. Among these alternatives,
biodiesel has gained importance in recent years for its ability to mix
with petroleum diesel. Biodiesel refers to a diesel-equivalent fuel
consisting of short chain alkyl (methyl or ethyl) esters, made by
transesterification of triglycerides, commonly known as vegetable oils or
animal fats. The most common form uses methanol, the cheapest alcohol
available, to produce methyl esters. The molecules in biodiesel are
primarily fatty acid methyl ester (FAME), usually created by
transesterification between fats and methanol. Currently, biodiesel is
produced from various vegetable and plant oils.

[0004] One by-product of the transesterification process is glycerin
(glycerol). For every 1 ton of biodiesel manufactured, 100 kg of glycerin
is produced. Historically, there was a valuable market for the glycerin,
which assisted the economics of the overall biodiesel process. With the
increase in global biodiesel production, however, the by-product glycerin
has saturated the market, which in turn has caused the market price of
the crude glycerin to fall. The valuable disposition of this crude
glycerin is vitally important to making the renewable biodiesel process
more efficient in carbon utilization while offsetting production costs.

[0005] Glycerin usage is primarily used in foods and beverages,
pharmaceutical and personal care, and fine chemicals. Glycerin is an
oxygenated three carbon chemical. With the rapid expansion of biodiesel
production, glycerin has become an abundant and inexpensive raw material.
This character brings glycerin in as a potential chemical building block
for other important renewable/green chemicals.

[0006] Two main classes of petrochemical raw materials are olefins
(including ethylene and propylene) and aromatics (including benzene and
xylene isomers), both of which are produced in very large quantities.
They are the building blocks of chemicals and plastics we are using
daily. These petroleum based commodity chemicals are not immune to
resource limitation and increasing cost that we face in the fuel industry
today. The search of alternative sources is vital important. The
strategic development for technologies in bio-chemicals and process
integration with biofuels could be similar to the current petroleum-based
processes. The building block chemicals must be relatively easy and cheap
to produce in large quantities. They should have chemical structures that
facilitate their conversion into multiple products of commercial
interest. Therefore, both bioethanol and glycerin have potential to be
the building block chemicals for petroleum-based ethylene and propylene
derivatives. The modernized biodiesel production enables the production
of glycerin in large quantities at very low costs, which qualifies it for
future development as one of the building block chemicals.

[0007] Propylene glycol is the preferred choice due to its established
market and large consumption. One particularly interesting propylene
glycol substitution is its use as a "green" non-toxic antifreeze and
de-icing fluid. Propylene glycol is currently produced from petrochemical
derived propylene. It has broad established market applications and
potential for other applications. The successful conversion of glycerin
to propylene glycol and the utilization of glycerin as a potential
petrochemical feedstock shall positively impact the biodiesel business
through better carbon utilization, by-product upgrade to high value
products, opportunity to develop renewable chemicals, and maximum return
on investment.

SUMMARY OF THE INVENTION

[0008] An aspect of the invention is directed to a process for converting
glycerin into propylene glycol comprising the steps of: preheating a feed
mixture comprising glycerin, hydrogen and methanol in a reactant heater;
passing the heated feed mixture to a reactor; separating the reactor
effluent into a vapor phase stream and a liquid phase stream; condensing
the vapor phase stream into a condensed liquid; recycling the condensed
liquid to the reactor; and distilling the liquid phase stream to obtain
purified propylene glycol.

[0009] The cost advantage for this glycerin based propylene glycol process
over petroleum-based propylene glycol production stems from its
simplicity. The glycerin-based propylene glycol production requires only
one process step whereas petroleum/natural gas-based propylene glycol
production requires multiple process steps.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 shows a process scheme for the conversion of glycerin into
propylene glycol in accordance with an embodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0011] A hydrogenation process is used to convert glycerin into propylene
glycol (PG). The process has greater than 95% selectivity to PG and
produces 98% or higher purity PG for industrial applications. An
exemplary process scheme is shown in FIG. 1.

[0012] An embodiment of the invention is directed to a process for
converting glycerin into propylene glycol comprising the steps of:
preheating a feed mixture comprising glycerin, hydrogen and methanol in a
reactant heater; passing the heated feed mixture to a reactor; separating
the reactor effluent into a vapor phase stream and a liquid phase stream;
condensing the vapor phase stream into a condensed liquid; recycling the
condensed liquid to the reactor; and distilling the liquid phase stream
to obtain purified propylene glycol.

[0013] The claimed invention is directed to a process for converting
glycerin to propylene glycol. The process scheme comprises a reaction
section to convert glycerin to propylene glycol and a fractionation
section to obtain on-spec propylene glycol product. A proprietary
catalyst is used comprising a metal or metal oxide dispersed on inert
support. The hydrogenation reaction of glycerin is carried out at a
temperature of approximately 190° C. and a pressure of 2.0-8.0 MPa
(20-80 atmospheres). One-pass glycerin conversion is greater than 70% and
propylene glycol selectivity is greater than 95%. The propylene glycol is
further purified in the fractionation section to meet various product
specifications.

[0014] An embodiment of the invention is directed to a process for the
conversion of glycerin to propylene glycol by hydrogenation in a fixed
bed reactor at a temperature of 150° C.-240° C. and a
pressure of 20-80 atmospheres. In certain embodiments of the invention,
the reaction temperature is approximately 190° C. In other
embodiments of the invention, the operating pressure of the reactor is
20-60 atmospheres.

[0015] In some embodiments of the invention, the hydrogenation of glycerin
to propylene glycol is performed by a supported catalyst in a fixed bed
reactor. In certain embodiments the supported catalyst is a metal or
metal oxide catalyst. In some embodiments the metal or metal oxide
catalyst comprises a noble metal, transition metal, or a combination of
transition metals. In certain embodiments of the invention, the supported
catalyst comprises copper.

[0016] As set forth in FIG. 1, in an embodiment of the inventive process,
a glycerin feed, along with hydrogen and methanol, is preheated in a
feed-effluent heat exchanger and reactant heater. The mixture then enters
the reactor where the hydrogenation of glycerin to PG takes place. The
reactor effluent, passes through a feed-effluent heat exchanger, and
enters a high pressure separator, where hydrogen and methanol are
separated from PG and glycerin liquid stream. The vapor phase is cooled
and the condensed solvent and boosted hydrogen are recycled to the
reactor.

[0017] In an embodiment of the invention, the liquid stream from the high
pressure separator is cooled down and de-pressurized before entering
distillation section. In other embodiments of the invention, the liquid
stream is depressurized and then cooled down. In an embodiment of the
invention, the reactor effluent is passed through three distillation
columns, column 1, column 2 and column 3, to separate the reactor
effluent into the following streams: fuel gas, methanol, mixed alcohols,
process water, acetol mixture (for recycle or product), 99.5% PG, PG/EG
mixture, and recycle glycerin. A first distillation column is used in
certain embodiments to separate fuel gas and methanol from the reactor
effluent. The effluent from the first distillation column is passed into
a second distillation column. The second distillation column is used to
separate alcohols, water and acetol mixture from the reactor effluent.
The effluent from the second distillation column is passed to a third
distillation column. The third distillation column is used to separate
PG, PG/ethylene glycol (EG) mixture and recycle glycerin from the reactor
effluent.

[0018] In an embodiment of the invention, a hydrogenation process for
converting glycerin into propylene glycol comprises a fixed bed reactor
loaded with a supported metal or metal oxide catalyst, where the majority
of glycerin in the feed is converted into propylene glycol. The reactor
effluent passes into a feed-effluent heat exchanger, and the vapor phase
stream is separated from the liquid phase stream. The vapor phase is
further condensed and the condensed liquid is recycled to the fixed bed
reactor. The liquid phase is further separated by distillation to obtain
purified propylene glycol.

[0019] In an embodiment of the invention, the fixed bed reactor can be one
fixed reactor, two fixed reactors in series, or multi-fixed bed reactors
in series.

[0020] In another embodiment of the invention, the fixed bed reactor is
operated at temperature of 150° C.-240° C., and pressure of
20-60 atmospheres.

[0021] In other embodiments of the invention the supported metal or metal
oxide catalyst that is used in the inventive process is selected from
noble metal, transition metal, or a combination of transition metals. In
other embodiments of the invention, the supported catalyst comprises
copper.

[0022] In an embodiment of the invention, the vapor phase stream is
separated from the liquid phase stream using a high pressure gas-liquid
separator. In other embodiments of the invention, the vapor phase stream
is separated from the liquid phase stream using a column with liquid
wash.

[0023] In an embodiment of the invention, the vapor phase stream contains
recycle solvent such as water, methanol, or other low boiling point
chemicals. In another embodiment of the invention, the recycle solvent is
a mixture of water and methanol. In a further embodiment of the
invention, the recycle solvent is mixed with a glycerin feed and passed
into the fixed bed reactor.

[0024] In an embodiment of the invention, a portion of the recycle solvent
and glycerin mixture is injected between two fixed bed reactors connected
in a series.

[0025] In an embodiment of the invention, the liquid phase stream is
depressurized and then cooled before entering a distillation column. In
other embodiments of the invention, the liquid phase stream is first
cooled and then depressurized before entering a distillation column.

[0026] In certain embodiments of the invention, multiple distillation
columns are used in the purification of propylene glycol. These
distillation columns can be selected from single shell column, column
with side draw, or divided-wall column.

[0027] In certain embodiments of the invention, a first distillation
column is used in certain embodiments to separate fuel gas and methanol
from the reactor effluent. The effluent from the first distillation
column is passed into a second distillation column. The second
distillation column is used to separate alcohols, water and acetol
mixture from the reactor effluent. The effluent from the second
distillation column is passed to a third distillation column. The third
distillation column is used to separate PG, PG/ethylene glycol (EG)
mixture and recycle glycerin from the reactor effluent.

[0028] In an embodiment of the invention, the by-products of the process
are separated by distillation. In certain embodiments, by-products are
mixed alcohols, water, ethylene glycol, acetol, and other trace
compounds. In certain embodiments of the invention, the by-product
ethylene glycol is a mixture of propylene glycol and ethylene glycol, or
high purity ethylene glycol. In other embodiments of the invention, the
by-product mixed alcohols contain water. In certain embodiments of the
invention, by-products methanol, water, acetol, and ethylene glycol are
obtained from side-draw at different distillation columns.

[0037] Although the present invention has been described in connection
with some embodiments, it is not intended to be limited to the specific
form set forth herein. Rather, the scope of the present invention is
limited only by the accompanying claims. Additionally, although a feature
may appear to be described in connection with particular embodiments, one
skilled in the art would recognize that various features of the described
embodiments may be combined in accordance with the invention. In the
claims, the term comprising does not exclude the presence of other
elements or steps.

[0038] Furthermore, although individually listed, a plurality of means,
elements or method steps may be implemented by e.g. a single unit or
processor. Additionally, although individual features may be included in
different claims, these may possibly be advantageously combined, and the
inclusion in different claims does not imply that a combination of
features is not feasible and/or advantageous. Also, the inclusion of a
feature in one category of claims does not imply a limitation to this
category but rather indicates that the feature is equally applicable to
other claim categories as appropriate. Furthermore, the order of features
in the claims do not imply any specific order in which the features must
be worked and in particular the order of individual steps in a method
claim does not imply that the steps must be performed in this order.
Rather, the steps may be performed in any suitable order. In addition,
singular references do not exclude a plurality. Thus references to "a",
"an", "first", "second" etc do not preclude a plurality.